Electrophotographic developing apparatus

ABSTRACT

Electrophotographic developing apparatus for applying a liquid developer to one surface of an electrophotographic recording element carrying the electrostatic image thereon so as to render the electrostatic image visible, the apparatus being adapted to apply liquid developer by a surface immersion technique and including edge control means arranged to contact portions of the recording element adjacent the side edges of the recording element as it moves past the reservoir containing the liquid developer, the edge control means preventing immersion of portions of the front surface of the recording element extending inwardly of the side edges for a predetermined distance whereby the back surface of the recording element is kept free from liquid developer.

United States Patent Nils L. Hakanson [72] Inventors 3,367,791 2/1968 Lein 118/637X West Springfield, Mass. 3,384,051 5/1968 Hunstiger 118/637 [21] Appl. No. 782,128 3,435,802 4/1969 Nail.., 17/37X [22] Filed 1 Primary ExaminerPeter Feldman I [45 Patented Attrneys-William J. Foley, Stanton T. Hadley, John W.

Kane, Jr. and Anthony J. McNulty [54] ELECTROPHOTOGRAPHIC DEVELOPING 1 g?. ABSTRACT: Electrophotographic developing apparatus for aims, 3 Drawing Figs.

applying a liquid developer to one surface of an electrophoto- U.S. recording element carrying the electrostatic image 1 17/37, 1 18/44, 1 l /4 thereon so as to render the electrostatic image visible, the ap- [51] Int. Cl Bb 5/02 params b i d t d to apply liquid developer by a surface Fleld 0f im er ion te hni ue and in luding edge control means at- 428, 44, 34; 95/89- 1 l ranged to contact portions of the recording element adjacent the side edges of the recording element as it moves past the [56] References cued reservoir containing the liquid developer, the edge control UNITED STATES PATENTS means preventing immersion of portions of the front surface 3,081,687 3/ 1963 Takats 95/89 of the recording element extending inwardly of the side edges 3,256,855 6/ 1966 Oliphant. 1 18/637 for a predetermined distance whereby the back surface of the 3,345,927 1 967 Takats 95/89 recording element is kept free from liquid developer.

J CF l 6| t 67 so 2 3 73 s3 68 3 70 54 57 66 j 5 l l l 64 7 I 58 ////JV //l/ /////\///)///l 48 74 62 PATENTEUJANZSIQYI 3.557.752

' SHEET 1 0F 2 m vmrl r m Nils L. Hokunson AHERNEY.

PAIENIEI]. mas |97l SHEET 2 [IF 2- INVENTOR. Nils L. Hokonson ELECTROPHOTOGRAPHIC DEVELOPING APPARATUS BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to apparatus for developing an electrostatic image carried on one surface of an electrophotographic recording element, and more particularly, to such apparatus of the surface immersiontype in which the recording element is guided so that one surface thereof is immersed in a liquid developer so as to render visible an electrostatic image carried on that surface. 7 Y

2. Brief Description of the Prior Art In the past, many different methods have been employed for applying a liquid developer to'a recording element so as to render visible a latent electrostatic image carried thereon. Such prior art apparatus was generally utilized for treating single sheets on an intermittent basis and even where it was used and associated with forming images on continuous webs, such webs were generally moved quite slowly or on an intermittent basis. A wide variety of ways of applying the liquid developer material to the sensitized surface of the recording element were employed. In some instances theentire recording element was immersed in the liquid developer and withdrawn and dried as by the use of heat and perhaps mechanical means such as squeegee rolls. In other instances, .the liquid developer was applied by spray techniques.

All of these processes generally result in application of the liquid developer not only to the front surface of the recording element carrying the electrostatic image but also to at least portions of the back surface of the recording element. This is It is a further object and advantage of the present invention to provide such apparatus which prevents immersion of portions of the front surface of the recording element extending T inwardly from the side edges for a predetermined distance.

especially true where the recording element is of the perforated type perhaps having holes therethrough to assist in folding the strip recording element as into afan-folded stack, or in separation of the strip recording element into a number of separate sheets, or for engagement of sprocket wheels by means of which, in some instances, the recording element is advanced through the processor or through subsequent apparatus. Because of the intermittent and relatively slow operation of these various forms of apparatus, the wetting of the back surface of the sheet did not cause problems since there was sufficient time allotted for the adequate drying of the sheet before it was utilized or further advanced through the processor.

However, with the advent of higher speed copying processes and particularly those associated with automatic data handling apparatus such as computer readout devices and microfilm copying devices, the speeds of copying have advanced to the point where drying capacity is inadequate if the back surface of the recording element receives any liquid developer. Such systems frequently operate at continuous speeds of up to 200 feet per minute and even higher. It is important in such circumstances to minimize drying capacity so that drying of the recording element can be accomplished in a reasonably short distance of say a few feet so that the process is useable in' a commercial office copier. This also results in the use of unnecessary amounts of liquid developer. The back surface of the recording element may be coated with a sealant of some type to prevent absorption of the liquid developer. However this surface will still be stained by the liquid developer which contacts it, which is undesirable. In addition, wetting of the back surface also tends to change the dimensional characteristics of the recording element which results in an inaccurate portrayal of the indicia being copied.

It is therefore a principal object and advantage of the present invention to provide electrophotographic developing apparatus for applying a liquid developer to one surface of an electrophotographic.recording element carrying a latent electrostatic image thereon so as to render the electrostatic image visible, which apparatus prevents any liquid developer from contacting the back surface of the recording element duringimmersion of the front surface thereof in said liquid developer.

SUMMARY OF THE INVENTION The invention is apparatus for applying a liquid developer to one surface of an electrophotographic recording element carrying an electrostatic image thereon so as to render the electrostatic image visible. The apparatus includes a reservoir containing a liquid developer and the reservoir has an inlet for the introduction of liquid developer and an outlet for the removal of liquid developer. A. pump is arranged to communicate with the inlet and the outlet to the reservoir and is adapted to circulate liquid developer through the reservoir. A backing member is disposed above the reservoir and is arranged to immerse the eleetrostatic-image-carrying front surface of the recording element in the liquid developer. The apparatus also includes edge control means arranged to contact the recording element as it moves past the reservoir so as to prevent immersion of portions of the front surface of the recording element extending inwardly from the side edges for a predetermined distance.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic elevation view of one embodiment of an integrated high-speed electrophotographic copying process illustrating the manner in which developing apparatus of the invention is utilized.

FIG. 2 is a sectional end view of developing apparatus of the invention taken along lines 24 of FIG. 1.

FIG. 3 is a sectional top view of apparatus of the invention taken along line 3-3.0f FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the high speed electrophotographic apparatus shown in FIG. 1, a recording element 10 in the form of a continuous strip is fed from a fan-folded stack 11, that is, a stack ll formed by the successive reverse folding of the recording element 10 along transverse lines equidistantly spaced along the strip. The recording element 10 generally comprises a base sheet which is generally paper but which may also be metal, plastic or the like and a photoconductive layer thereon which in most instances comprises a homogeneous mixture of a filmforming resin containing photoconductor particles. The filmforming resin may be, for example, silicone resin, polyvinyl chloride resin, polyethylene, phenolic resins, polyester resin, methacrylate resin, polystyrene resin, styrenated alkyd resins, or vinylacetate-vinylchloride copolymer resin. The preferred photoconductor is zinc oxide such as, for example, the photoconductive zinc oxide sold by the New Jersey Zinc Company as Florence Green Seal 8. The photoconductor particles can be any known photoconductor such as the oxides of zinc, antimony, aluminum, bismuth, cadmium, mercury, molybdenum and lead; the iodides, selenides, sulphides or tellurides of these metals; selenium, arsenic trisulfide, lead chromate and cadmium arsenide. It is also contemplated that various types of organic photoconductors might be used. These materials have been recently developed and are well known to those skilled in photosensitive resins.

The surface of the recording element 10 which is photoconduc ive is the surface containing the electrostatic image to be developed and will be referred to throughout this application as the front surface." The opposite surface of the recording element 10 will be referred to throughout this application as the back surface."

The recording element 10 passes over a guide roll .12 and under a guide roll 13 and over another guide roll 14 and is advanced under tension between two charging grids 15 and 16 of a corona discharge unit 17. The grid 15 is positively charged, while the grid 16 is negatively charged. The recording element 10 issues from between the corona discharge grids l5 and 16 with a uniform electrostatic charge on its upper or front surface. It passes beneath a guide roll 18 and is advanced in tension to another guide roll 20 across a flat plate 21. Preferably, a slight vacuum is applied by the flat plate 21 to the-back or uncharged surface of the recording element l to insure that the recording element lies in the plane of the flat plate 21 during exposure to an image. Such a vacuum may be applied by attaching a vacuum source (not shown) to the back side of the plate 21 and providing perforations (not shown) through the plate 21 so that the vacuum communicates to the front surface of the plate 21 through such holes or perforations and draws the recording element 10 into contact with the plate 21.

A latent electrostatic image is created on the recording element [0 as it moves over the plate21 by exposure of the front surface thereof containing the photoconductive material to a pattern of light and shadow illumination. Such a pattern may be created as by moving a strip 22 of film which may be microfilm fed from the reel 23 to the reel 24 past a light source 25. The film 22 contains the image which is to be copied and the light source 25 projects the image through a lens system 26 and onto the front surface of the recording element 10. The lens system 26 may be provided with means for enlarging the light image to the desired size. When the pattern of light and shadow illumination contacts the front surface of the recording element 10, the illuminated areas of the surface are discharged and a charge image remains which corresponds to the shadow pattern presented to the sensitive recording element 10.

This latent charge image is then developed by means of the developing apparatus of the invention, indicated generally by reference numeral 27, which will be specifically described with reference to FIGS. '2 and 3 of the drawings. However, it should be noted that the front surface of the recording element 10 is immersed by the developing apparatus 27 in a liquid developer.

The liquid developer may comprise any one of the conventional types of toner materials utilized which generally comprise finely divided pigment particles carried in a carrier solution, the pigment particles being of a nature enabling them to receive a triboelectric charge thereon of a predetermined polarity so that they tend to gravitate toward a charged image portion of the recording element 10 so as to develop that image and render it visible. Such liquid developers are well known to those skilled in the art of photocopying processes of the electrostatic type.

The recording element 10 is withdrawn from the developing apparatus 27 and passed through a squeegee nip 28 formed by two squeegee rolls 30 and 31 which remove excess liquid developer from the-front surface of the recording element 10. The recording element 10 is then advanced through a dryer section 32 of the apparatus in which it is entrained about a heated roll 33 and suspended for a short distance and then entrained about a subsequent guide roll 34. A hood 35 is disposed over the portion of the recording element 10 contacting the heated roll 33 and over the suspended portion extending between the heated roll 33 and the guide roll 34. The hood 35 is adapted to receive air at the inlet 36 which air is heated by heaters such as electrical resistance elements located in the section indicated by reference numeral 37. This heated air is emittedover'the front-surface of the recording element 10 in generally countercurrent flow, most of it being removed from the hood 35 at the point beneath the heated roll 33 and adjacent the squeegee rolls 30 and 3l.-A fan (not shown) may be employed at the inlet 36 to drive the air through the hood 35 or the air may be fed into the hood 35 under pressure. This drying section 32 removes most or all of the residual volatile components of the liquid developer from the recording element 10, leaving the recording element 10 entrained over the guide roll 34 substantially dry. The resulting recording element 10 containing the developed image thereon may be refolded into a fan-folded stack 38 and transferred to another position for ultimate use. The refolding is accomplished by a pair of rolls 40 and 41 which feed the recording element 10 downwardly in a fashion such that it reassumes its original fan-folded condition.

FIGS. 2 and 3 illustrate the developing apparatus of the invention in greater detail. Looking at H68. 2 and 3, it can be seen that the apparatus has an outer catch basin 42 having an inwardly and downwardly sloping bottom leading to a drain 43. The drain 43 communicates through a pump 49 to an inlet duct 44 which leads into the bottom of an inner tank 45 which serves as a reservoir for liquid developer and is disposed above and within the catch basin 42. The inlet duct 44 passes through the sloping bottom surface of the catch basin 42 and a seal is maintained between the duct 44 and the bottom surface of basin 42 by an Oring 46 carried in a mounting 47 secured to the bottom surface of the catch basin 42. The relative height of the inner tank 45 is adjustable by screws 48 disposed on either side of the tank 45 and threadedly attached to flanges 50 depending outwardly from each side of the inner tank 45 and bearing against a lower flange 51 depending inwardly from each side of the catch basin 42. This permits the inner tank 45 to be moved up and down relative to the catch basin 42.

A baffle plate 52, which may comprise an imperforate metal plate is positioned generally over the inlet duct 44 at the point where it enters the inner tank 45 and from one side of the inner tank 45 to the other side. The baffle plate 52 serves to distribute liquid developer entering the inner tank 45 from the inlet duct 44 so that it does not impinge directly against the surface of the recording element 10 above it. The baffle plate 52 has a dimension in the direction of travel of the recording element which is less than that of the inner tank 45 so that liquid developer is free to surround the baffle plate 52 and to circulate over the immersed surface of the recording element 10. ln practice, the liquid developer is pumped into the inner tank 45 until it overflows over the sides thereof. The liquid developer overflows into the catch basin 42 and is then recirculated by means of the pump 49. The catch basin 42 may also be used as a reservoir for additional liquid developer or a separate additional reservoir (not shown) may be supplied. Additional liquid developer may be added to the system either into the catch basin 42 or into another reservoir (not shown) or into the duct connecting the catch basin 42 to the pump 49, as by insertion at the point indicated by the arrow 53.

The recording element 10 is fed over the upper surface of the liquid developer carried in the inner tank 45 and has its lower surface, that is, its front surface carrying the latent electrostatic imagethereon, immersed in the liquid developer carried in the inner tank 45 so as to develop that image and render it visible.

A backing member indicated generally by reference numeral 54, is disposed above the recording element 10 and is fixed to the side plates 55 and 56 which also carry the catch basin 42. Thus, the height of the backing member 54 relative to the catch basin 42 is fixed. The backing member 54 comprises a top plate 57 on one side of which is hingedly attached to the side plate 56 by means of a pin 58 connecting a flange 60 on the top plate 57 to a flange 61 depending inwardly from the side plate 56. The opposite end of the top plate 57 rests on an angle bracket 62 depending inwardly from the side plate 55. Two comb members 63 and 64 are secured to the lower surface of the top plate 57 and are adapted to contact the back surface or top surface of the recording element 10 with their lower surfaces as the recording element 10 passes over the inner tank 45 and to form a flat supporting grid surface over which the recording element 10 slides. In order to provide for varying width of the recording element, the comb members 63 and 64 are moveable relative to one another and have a lurality of spaced elongate elements 65 which interfit with similar elements 65 of the other so that the width of the surface of the backing member 54 may be increased by pulling the comb members 63 and 64 apart and yet a broken or gridlike but substantially evenly supporting surface is still maintained by the two comb members 63 and 64, as shown in FIG. 3. The comb member 63 is fixed to the top plate 57 while the comb member 64 is moveable relative to the top plate 57, its sliding support being accomplished by pin members 66 having knobs 67 on the upper ends thereof which pass through slots 68 in the top plate 57.

The liquid developer is initially brought into contact with the lower or front surface of the recording element 10 by raising'the inner tank 45 to a point sufficient to cause the liquid developer therein to contact the recording element 10 before it overflows from the inner tank 45 and into the catch basin 42.

In accordance with the invention, edge control means 70 are provided which contact the recording element 10 as it moves past the inner tank 65 or reservoir containing the liquid developer. The edge control means 70 prevent immersion of portions of the front surface of the recording element 10 extending inwardly from its side edges for a predetermined distance. In the embodiment shown, these edge control means 70 comprise an elongate flange member 71 having an upstanding rib 72 which emerges above: the surface of the liquid developer in the inner tank 45 and hence above the edge of the inner tank 45 for a distance sufficient to raise the side edges of the recording element 10 above the level of the liquid developer contained in the inner tank 45 .This prevents wetting of the portions of the recording element l which are elevated by these upstanding ribs 72 which is important in that these prevent leakage of liquid developer. over the side edges of the recording element and onto the back surface thereof which would otherwise occur. Such a provision is extremely important where the recording element 10 has holes along each side edge, as where it is adapted to be sprocket fed through processing apparatus such as perhaps through the apparatus shown in FIG. I. I

In accordance with the invention, these edge control means 70 are moveable relative to one another so as to permit their use with recording elements 10 of different widths. It also permits adjustment of the amount of the recording element 10 which is to be kept out of contact with the liquid developer. 1

Thus on one side, the flange 71 is fixedly attached to an elongate angle 73 which is carried at each end by spaced brackets 74 rotatably carried by the rotatable rods 75 and 76. The rods 75 and 76 are rotatably carried by the side plates 55 and 56. Movement of the brackets 74 along the rods 75 and 76 is prevented by collars 77 on the rods 75 and 76 which are fixed thereto. The rods 75 and 76 contain threaded portions 78 and 80, respectively, along their opposite ends and the flange 71 on that side is also carried by an elongate angle 81, each end of which is carried by a. bracket 82 threadedly mounted on the rods 75 and 76. These rods75 and 76 are rotatably affixed together as by a belt 83 passing over pulleys 84 and 85 disposed on the ends thereof, respectively, and affixed thereto so that upon rotation of the rod 75, the other rod 76 also rotates an equal amount, thereby assuring that the position of the moveable upstanding rib 72 remains parallel to the stationary upstandingrib 72. The rod 75 may be turned as by a knob 86 affixed to the opposite end thereof.

It has been found desirable to utilize an electrical bias voltage in the developingapparatus to assist in the development of the latent electrostatic image. In this regard, the top plate 57 of the backing member 54 is normally made of insulating material while the comb members '63, and 64 are made of an electrically conductive material to which a biasing direct current voltage may be applied. The voltage may be of either a positive or negative polarity depending upon the triboelectric properties of the particular photoconductive particles utilized in the liquid developer. The inner tank 45 is normally electrically grounded so as to complete the circuit from the comb elements 63 and 64 through the recording element 10 and through the liquid developer to the inner tank 45.

Thus it can be seen that the invention provides apparatus for applying a liquid developer to one surface of an electrostatic recording element without getting liquid developer on the back surface thereof. The apparatus of the invention also makes it possible to hold predetermined portions of the recording element adjacent the sideedges thereof out of the liquid developer so that if such portions'contain perforations,

no wetting of the back surface will occur due to passage of liquid developer through the perforations.

From the above, it can be seen that many changes and modifications can be made in the apparatus described above without departing from the'spirit and the scope of the invention. For example, both of the edge control means might be moveable laterally. Similarly, the inner tank might be stationary and the backing member might be moveable so as to press the recording element into the liquid developer. in view of the numerous changes which might be made to the particular embodiments described above, the invention is not intended to be limited to these particular embodiments except as may be required by the following claims.

I claim:

1. Apparatus for applying a liquid developer to one surface of an electrophotographic recording element carrying an electrostatic image thereon so as to render said electrostatic image visible, comprising:

a reservoir containing a liquid developer, said reservoir having an inlet for the introduction of liquid developer and an outlet for the removal of liquid developer;

a pump communicating with said inlet and said outlet and adapted to circulate liquid developer through said reservoir;

a backing member disposed above said reservoir and arrangedto immerse the electrostatic-image-carrying front surface of said recording element in said liquid developer; and

edge control means arranged to contact the recording element as it moves past said reservoir so as to raise the side edges .of the recording element above the level of the liquid developer to prevent immersion of portions of the front surface of said recording element extending inwardly from the side edges for a predetermined distance.

2. Apparatus according to claim 1, including a baffle member disposed in the liquid developer in said reservoir and between the front surface of said recording element and said inlet, whereby the flow of liquid developer being introduced at said inlet is distributed throughout at least a portion of said reservoir.

3. Apparatus according to claim 2, wherein said inlet is located at the bottom of said reservoir, and said baffle member comprises a flat plate, said plate extending substantially from one side of said recording element to the other and disposed beneath the front surface thereof.

4. Apparatus according to claim 1, wherein said backing member is arranged to vary in width depending upon the width of said recording element.

5. Apparatus according to claim 4, wherein said backing member comprises at least two parts, each of said parts having a plurality of elongate elements which interfit with corresponding elements on the other part, said parts being adapted for relative movement therebetween so as to permit the effective area of said backing member to vary depending upon the width of said recording element.

6. Apparatus according to claim 2, wherein said baffle member and said reservoir are electrically connected to ground potential, and said backing member is electrically connected to a direct current potential.

7. Apparatus according to claim 1, including means for adding additional liquid developer to said reservoir.

8. Apparatus according to claim I, wherein said edge control means are adapted to cooperate with said backing member so as to hold said portions above the surface of said liquid developer.

9. Apparatus according to claim 1, wherein said edge control means comprise an elongate element extending along each side of said recording element, said elongate element having an upstanding rib portion extending above the surface of said liquid developer, said rib portion being adapted to prevent wicking of said liquid developer outwardly beyond said edge control means is mounted for lateral movement relatively toward and away from the other to permit the handling of recording elements having different widths. 

2. Apparatus according to claim 1, including a baffle member disposed in the liquid developer in said reservoir and between the front surface of said recording element and said inlet, whereby the flow of liquid developer being introduced at said inlet is distributed throughout at least a portion of said reservoir.
 3. Apparatus according to claim 2, wherein said inlet is located at the bottom of said reservoir, and said baffle member comprises a flat plate, said plate extending substantially from one side of said recording element to the other and disposed beneath the front surface thereof.
 4. Apparatus according to claim 1, wherein said backing member is arranged to vary in width depending upon the width of said recording element.
 5. Apparatus according to claim 4, wherein said backing member comprises at least two parts, each of said parts having a plurality of elongate elements which interfit with corresponding elements on the other part, said parts being adapted for relative movement therebetween so as to permit the effective area of said backing member to vary depending upon the width of said recording element.
 6. Apparatus according to claim 2, wherein said baffle member and said reservoir are electrically connected to ground potential, and said backing member is electrically connected to a direct current potential.
 7. Apparatus according to claim 1, including means for adding additional liquid developer to said reservoir.
 8. Apparatus according to claim 1, wherein said edge control means are adapted to cooperate with said backing member so as to hold said portions above the surface of said liquid developer.
 9. Apparatus according to claim 1, wherein said edge control means comprise an elongate element extending along each side of said recording element, said elongate element having an upstanding rib portion extending above the surface of said liquid developer, said rib portion being adapted to prevent wicking of said liquid developer outwardly beyond said rib portion toward the side edges of said recording element.
 10. Apparatus according to claim 1, wherein at least one of said edge control means is mounted for lateral movement relatively toward and away from the other to permit the handling of recording elements having different widths. 